1. Field of the Invention
The present invention relates to a work vehicle equipped with an engine as a driving source, which performs work such as cargo handling and public works construction.
2. Description of the Related Art
In an engine forklift, because a single engine serves as the driving source for both the cargo handling system and the traveling system, an engine having a high engine output is used.
This raises problems, such as deterioration of energy efficiency and increase in exhaust gas when the engine is running at a low rotational frequency.
When an engine having a small output is used in order to eliminate these problems, it becomes necessary to disconnect the traveling system or the cargo handling system from the engine under high load conditions. Accordingly, there are restrictions on usage.
As a solution to such problems, as is disclosed, for example, in Patent Citation 1 and Patent Citation 2, there has been proposed a so-called a hybrid system in which an engine and a motor/generator are jointly used as the driving source.
The invention disclosed in Patent Citation 1 is configured in such a manner that the traveling system and the cargo handling system are driven separately by independent electric motors. The engine generates electric power by driving the generator and so charges the battery at the same time. Each of the electric motors for the traveling system and the cargo handling system is driven by electric power generated by the generator or electric power discharged from the battery.
The invention disclosed in Patent Citation 2 is configured in such a manner that the traveling system is driven by an electric motor and the cargo handling system is driven by the engine and a motor/generator. The electric motor is driven by electric power discharged from the battery. The battery is charged by excess electric power of the motor/generator driven by the engine and regenerative electric power from the electric motor.
In the inventions described in Patent Citation 1 and Patent Citation 2, the engine charges the battery under low load conditions, which eliminates the need to lower the rotational frequency. It is thus possible to improve fuel efficiency and lower the amount of exhaust gas.
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2003-250203
Patent Citation 2: Japanese Unexamined Patent Application, Publication No. 2000-313600